This invention relates to an electric valve actuator having a failsafe system for use in a rotary valve.
Many rotating valves are operated by actuators that rotates the valve 0-90xc2x0 to open and 90-0xc2x0 to close. The actuators can be electrically operated (motor, pinion, gear), hydraulically, pneumatically, or pilot operated. When fast acting is required the electric motor with mechanism is usually slow to open or close as compared to hydraulic, pneumatic, or pilot operated valves.
Hydraulically operated valves require hydraulic power and control valves, linear actuators and linkages, or rotary actuators to rotate the valve 0-90xc2x0. This tends to make the valve package large since a hydraulic power source is required.
Pneumatic valve operation (using air) requires a compressor line, regulators, control valves, and linear or rotary actuators with the response limited to the compressor, flow and pressure, and exhaust lines.
Pilot operated valves use a solenoid pilot valve that directs the gas pressure of the gas line to an actuator that rotates the valve. A minimum pressure is required to operate the valve and an external venting line needs to be added to release gas flow used by the pilot valve.
A spring return is usually required for a failsafe operation in all of the above mentioned designs. The implementation of the spring is packaged in the hydraulic, pneumatic, and pilot operated systems. In a mechanical system with electric motor, the spring packaging tends to be complicated and usually another external power source is required.
This invention presents an alternative to the above mentioned designs by providing an actuation method that allows operation of a rotary valve through a direct coupling mode with a failsafe spring for fast actuation and safe operation. This invention avoids the use of external gas leakage lines, external power sources, or hydraulic power by providing a motorized valve with a fast failsafe mechanism in the event of power failure.
It is therefore an object of the present invention to improve the electric type actuation of rotary type flow control valves.
It is a further object of the present invention to improve the safety of rotary type flow control valves.
Another object of the present invention is to more rapidly close a motor driven rotary type flow control valve in the event of a power failure.
A still further object of the present invention is to improve failsafe devices for closing a rotary type valve in the event an emergency situation is sensed.
These and other objects of the present invention are attained by means of a failsafe device for use in a rotary type control valve that includes an electrical drive motor having an output that is coupled to a drive shaft through an electric clutch. The drive shaft is arranged to turn a cam cylinder which, in turn, rotates the stem of the control valve. A cam profile is provided in the cam cylinder and a cam follower that is slidably mounted on the drive shaft traces the profile of the cam as the valve moves between a fully closed and a fully open position. A series of torsion springs are connected to the cam cylinder so that the springs are wound to a loaded or energy storing condition as the valve is turned from a closed position to an open position. In the event of a power failure the clutch disconnects the motor from the drive shaft and the springs arc allowed to unwind and thus turn the cam cylinder so as to close the valve. During this time, the cam follower controls the motion of the cylinder during the closing sequence.